Method and means for eliminating fading on short wave lengths



Aug. 30, 1932. H. H. BEVERAGE ET AL METHOD AND MEANS FOR ELIMINATINGFADING 0N SHORT WAVE LENGTHS Filed March 15, 1928 z/M/rrk- Mow/MmeINVENTORS H H BEVERAGE BY PE RSO" flc/acu A ORNEY Patented Aug. 30, 1932UNITED sr 'ri-is HAROLDH. BE ER GE AND HARO D PETERSON, ornrvnnmmn;.ivnw Yonm-Asj smnons'ro RADIOCORPORATION OF'AMERIGA, a CORPORATION orDELAWARE mn'rnon AND MEANS FOR ELIMmA'riNe minute on SHORT WAVE Lmre'r sI.

1 Application filed man 15,- 1928. serial-no- 261,736.

':,The invention relates to what is commonly known as fading in radioand wireless signalling and a method and means for eliminating thedetrimental effects thereof. The r, invention particularly adapts itselfto the any appropriate and desired type of short wave radio signallingapparatus and lends itself especially to use in locations where the 10effects of fading and troublesome. p

Various theories have frequently been suggested for explanations of thephenomenon f known as fading, but it is believed thatto date nothoroughly proven theory has been developed. However, certain evidencesand phenomena in connection with lfading have been discovered inpractical observation f which have brought out the factthat short. wavesignals fade difierently at? points separated by short distances andthat the phase relation between signal voltagesat; these points has beenfound to be reversed several times per minute, --In accordance withthese observations, it hasbeen found that signals have different fadingcharacteristics when picked, up on antennae located atv different.points or upon antennaelocated at the same.

point, where the antennae each have difi'erent '30 directivecharacteristics. If two antennw are been found that the phase relationbetween v10100 ft. away, does not remainconstant, from moment to moment.Therefore-if it is tried to combine a radio frequencyvoltage from arepraticularly prevalent relationships atthe several antennae, and;

.connection with the QWl1QIG1I113-i Fig. 1 .jillustra-tesa: preferredmeans for combining the rectified signals from aplu instant may be ofminimumintensity upon up upon the several antennasystems 1n ques-;

tion, to some common receiver and add the,- energies directly togetherat this point, but a this cannot be done efficiently because it has Ithe signal voltage received at one antenna and that received at another1 antenna,- say two or more antenna systems located. at:

points several wavelengths apart, it will be found that these voltageswould add at one instant and subtract at another instant due to the factthat the radiofrequency voltages at the two antennaewill not hold a Vrecelving of short waves as transm tted from definitefphase relationshipwith respect to each other. However, where the receiver is rapidlyswltched from one antenna system to anotheras disclosedin our copending'applicationslSerial Nos. 2 61, 757v filed March 15, 1928, and 274,374,filed May2, 1928, efficient results areobtainable,but this is not adirect combining action 4 i 1 The important principles to be followed'inthe multi antennae anti-fading ,Qmethods,-, which forms a principalobject of this invention, is to combine the signals fromtheplu rality ofantennae insuch a way. that the energies will addirrespective'ofthephase combine in such aimanner that a signalinay r beheard or'recorded in a suitable recordlng deviceto produce a signalwhich "is substanfading on any of the several antennae. The above andother objects form the purpose of this. invention which will be morethoroughly understood. by making reference ltially free from thedetrimental effectsjof to the following specification when readinaccompanying drawing,

rality ofg'spaced antennae. U:

Fig. 2indicates a system similar tothat;

shown in F ig. 1 wherein two antennaeiof different directivecharacteristics, which correspond to the spaced antennaeof Fig.1,arelocated ata common point and the energy from'the combined output isdirected to a limiter and modulator' device for thepurpose of obtainingatone signal; and, w

Fig. 3 illustrates; results which may be accomplished by the eifortsandarrangement functioning in accordance with the apparatusdiagrammatically illustrated ingFigsl and 2. The Q subject matter ofthis application forms a continuation in part of oumop nding applicationfiled January 2, 1926, Serial i as frequency energy reaching antennae 1and 3 .is transferred to radio frequency transformers, or any otherpreferred formiof cou-Y plings', 9 and 11 and carried through leadcircuits 13 and 15 respectively I to; receiving devices generally shownas 17 and 19 for each of said separated antennae member's; I The re- 1ceivers 1'7 and 19 may each employ a common oscillator as shown by Fig..3 of Serial #7 8,7 68, above referred to, or each receiver 3 17 and 19may be provided with an independ ent oscillator, or the energy receivedupon antennae 1 and 3 may be detected in the receiver 17 and 19 in theusual manner'without the need of oscillator.

The output 'of The energy from the amplifiers :21 and 23' is directed tothe primary'windings 29 and- '31 of the transformers 25 and 27, fromwhich 7 it is transferred to the secondaries 33 and-'35 and directed tothe rectifiers 37 and 39, which "each may be biased by a commonpotential j source 19." If desired, the filaments 43 and i 45 may beconnected in parallel and" ener-' gi'zed from'a singlefilament batterydesi g f nated' l7. Y V In'series with the common bias potential suipply19 for the pl'atemembers' of the rec to rectified energy pulses and,therefore; does not difierentiate' between the phase 'reers 37 and 39 isa recording device, geni of the 'drawing,'we have illustrated the'formerally designated 41, which only responds lation of the radiosignalinput upon the two 'receivers 17 and 19. It is, therefore; seen that therecorder 41 responds; only tothe I. energy andthe matter ofphaseflrelationship of the signals reaching the antennae 1' and 3i isimmaterial and has no effect upon there sults produced in the recorder41. I

.As above describedfor producing a rew cording action in 11 it isassumed that the L I switches indicated as 51 and 53 in the platecircuits of thetubes 37 and 39:respectivelyi are closed. .However,-forthe purpose of determining the separate energy reaching eachof therecelving ClICLlltSflIlClUdlIlg the tubes 37 and 39 we have provided ameans for in-,

dicating this energy by the separate recorders designated asRl and R2.In a case where this energyis desired the switches designated as 51 and53 may be" opened "and the switches 55 a nd 57 closed, so that an energyresponse from each of the signals may be recorded in the recorders BlandR2. 7 This switching only resorted to'for eXperi-.

the receivers 17 and 1'9is amplified in any preferred manner by the useof amplifiers generally designated 21 and mental purposes and for thepurpose of determining the separate energy'received.

By Figure 3 of the drawing we have shown the result which may beexpected by receiving signals on each ofthe separated antennae'members-and represents a P01131011 of typicalsignal which might bereceived. by placing the recorder R1 or R2 in series with the platesoftubes 37 and 39... To specifical- .lyrefe r'to the part ofEig'Q 3,1lettered'asfA,

it-will be noted that'the part (Pof the on receiver 17 and recorder R13"but' at'a "different time interval d1 had completely faded out in therecorder R2 associated with the antenna system 3. However, the portionCof the tape illustratedby Fig. 3 shows the combined signals receivedfrom the two antenna systems land 3' in the recorder 11;

and it will be noted that by combining the energy pulses which aretotally independent of the phase of the signals reaching the antennasystems 1 and 3thata signal has been recorded which is'accur'ateand thatallpor tions'of the same are clearly legible with'the effects of fading''on either of the antenna numbers 1 or 3 substantially eliminated.Thesetapes shown byffFig. '3 illustrate the results, which have actuallybeen 'found in practice and are drawn from actualrecords which .havebeen madein practice using the 'ahovedescrib'ed arrangement.

To "now make; specific reference to 2 located at the same point,and', asshown, 101

represents a vertical doubletand 103a horizont al doublet'both locatedat the 'samere ceiving point; and whose respective charac-.

teristics vary due; to-their directive characteristics. "Energy from thevertical doublet 101 is directed to aradio frequency amplifier 105,which has not been shown in connection with 'Fig. 1' although it is tobe understood that such amplifier may be added and used if desired.Fromthe amplifier 105-the energy is directed to a receiver 109 wherethe;incoming signals are detected andamplified through an audio frequencyamplifier 113' and transferred through the primary winding 1210f atransformer'conne'cted withthe audio frequency amplifier to: thesecondary feeding its energyfinto the rectifying tube 129. 'Sirhilarl-y,the energy received on "thehoriziontal doublet103 is fed to the radiofrequency 'ainplifierQlO'Z to the receiver 111 and then tlirtjnigh theaudio frequency plifier which transfers its output energy to .passed tothe rectifying'tube 131.

winding 123 of the transformer 119, Where the energy is thentransferredto the secondary 127 of the transformer .119 and Therectifying tubes 129 and 131 are shown as the-single filament, doubleplate type, but

two single'plate rectifiers may'beused with 1 equivalent results.Byfusing full wave rectification, the pulsations of direct current aremore uniform, and theripple' frequency :is double the audio inputfrequency, both'of 'which effects make it easier to produce a puredirect current in the rectifier output. It is desirable to substantiallyeliminate the ripple in the rectified current, since strong ripples tendtofvib'rate the recorder pen, and

v also beat reactions between theripples'may produce undesirablevariations when theoutputs o f'a plurality of rectifiers arecombined.

The ripples maybe eliminated by using condensers such as are commonlyusedacross recorder coils. However, for high speed operation, thesecondensers'tend to reduce the signaling speed, and it would bepreferable to use low pass filters. These filters should readily passthelow'frequenc'y corresponding to the keying pulses, but should not passthe relativelyhigh ripple frequency.

In Figure 2, the low pass filters 139 are j shown as a conventionalarrangementof series inductanceand shuntcapacitance ele- 'men'ts. Afterthe rectified current has passed through filter 139, a substantiallypure 1distantially identical to that of Fig. 1' with the exception ofthe fact that instead of using the spaced antennae 1- and 3 of Fig. 1 wehave 7 R and R of Fig.1 be connected in series,

chosento illustrate antennae 101 and 103 of I different directionalcharacteristics located;

at the same point. If a recorder such as with the circuit atpoints 189and 1910f Fig. 2, the results and the records obtainable will besubstantially the same as are illustrated by the records A and Bof'Figl3 above I described. The combinedrecord C ofFig. 3 would beobtained if a recorder were substitute'd in place of resistance 135.

'In Figure 2, we have chosen to show a modification which maybe used forobtain ing a tone signal afterjthe rectifiedcurrents have been combined,andwhich will also pro duce a certain amount of limiting action which isdesirable, sinceitreduces the effects of small variations in thecombined rectified currents. The arrangement which is enclosed withinthe dotted line rectangle is the limiter and "modulator arrangement usedfor the *purpas'e 6i] teaming a tone's'ignal in the tone circuit 17 5to. bevhereinafter described.

The ungrounded'end of resistance is connected through a bias battery 141to'fthe grid member 147 o'fthe triode 14-3. The triode 143 has itsenergy andhigh potential-supply the filamenfimember 149, which is;grounded at 155.; The -grid-member 147 of the til-be 143 is normallysobiased by battery 141 that plate current willflow under conditions whenno signal 'is being received. this case,

plate current flows thru' the plate*',-the:

filament 149, the batteryv151 and the resistrO-r the plate 145furnishedthrough a'battery 151 connected in series with a resistance 153. Theplate circuit is completed through ance-153. However, wh'en's'ignals-arebeing 7 received upon the antennae 101' and 1O3 -ajnd directed from the"points 189 and 191 of*the 'rectifiers 129 and'131,' to the .p0int1133,due:

to the voltage drop occurring across-the resistance 135, the point 133-becomes negative with respect to its previous potential, and thereforethe normal bias on the grid 147 of the tube 143 is-overcome. It is'to beunder stood thatthe cut-oft potential of thetube 143 depends upon boththe voltage andpolarity ofthe bias battery 141, and the characterifsticsof the tube 143. It is also to beseen that when where resistance 153forms a connection with the plate 145 of the tube143 and the biasbattery 157 for the grid 163' ofithe tube..1"59

that this grid 163 becomes negative; due to the voltage drop occurringacross resistance 7 the tube '143'is passing plate current that thepoint" 153. In this case, with no signal :on, the grid i 163 of the tube159, is carried to .cutoffpotential and the tube 159 fails-to passEplate" current. However, when the -'plate-current flow through thetube1143' is cut. ofl'due to signals being received upon the antenna members.101 and 103 and the point 133. ofthe resistance 135 becoming negative,r the bias battery. 15? carries the. grid member 163 of the. tube 159to, a'less negative valueland the tube 159 at once starts to passaplatecurrent, through'the plate member 161, the filament 165, the groundreturn 167 v and 179 and the plate potential supply 17 7; Connected tothe lead with the plate supply source17'lthrough a transformer 181* isan-audio sfrequencyos- -cillator- 187 which feeds its energy into theprimary 183 of the transformer- 181 from which the-energyis transferredto the sec- I ondary 185. Also connected-in theplate lead 161 is atransformer 169having its primary winding 171 forming a part i of theplate circuit and secondary 173 transferring 'energy to a tone circuit175. It isthus seen'that the frequency of the audio oscillato'r 187 isheard in the tone circuit 17 5 during periods when the tube -159 ispassing 'platecurrent, or in other words, at periods when signalsare 55dlrective cha-racter1st1cs, or combinations of being: f p n either ofthe antenna members r'103; a c

It may thus 'belnoted that thejfunctioning the limitingand modulatingarrangement illustrated inthe dotted line rectangle asa partof 'Fig. 2is determined by the fact of [how negative thepoint183 becomes and howthis' eifects the grid 147 of the. tube 143, since it is thischaracteristic which determines Ewhether or not the tube 143 passesplate current, .and likewise the size of the resistance 153 and thebattery .157 which it will be noted 2 should be of a size approximatelythe same as the battery 151-determines whether or not .the .itube l 59passes plate current. It will also'be noted that if the limiter isadjusted so that the minimum'signalwill make the point 183 sufiiciently,negative to a reduce the plate current of tube-1l8 to .zero, a furtherincrease in signal will haveno eifect on the 7 tone output oftransformer169. Hence, if 1 the combined rectifier currents vary overmoderate limits, when proper adjustments 1 are made these variationswill not be repeated throughto tube 159 which controls the tone output.

With further reference to Fig. 2, if the radio frequency amplifiers 105and 107. are capable of delivering considerable energy, it. -is notnecessary to convertthe signal to lower frequency, as the output of theradio fre- .-quency amplifiers mayberectified directly :by rectifiers129 and 1 stages of radio frequency amplification with 131. By usingseveral several tuned circuits, a highdegree of selec tivity may beobtained. Such an arrangementwould make it easy to filter the rectifiervoutputs, and this would make it particularly quency.

" desirable for very high speed circuits, where the keying frequency maybe several hundred cycles. It would also be desirable in somecases-toconvert the signalto an intermediate radio frequency instead of an audiofrei This may be accomplished by substituting intermediate frequencyamplifiers in place of the audio frequencyamplifiers 113 "and 115. ;'Thefundamental operation would be substantially'the .same as that described6 in connection with Fig. 2.

While only two receivers 5 by Figs. -1 and 2,itis to beunder'stood thatanynumber of receivers be used, using combinations of spaced antennae ofthe same type, combinations of antenna withdiiferent Y v both spaced anddirective antennae. It has been determined"experimentally that a particularly desirable combination of spaced antennaefor short waves,'forexample 15gt o 30 meters, isto use three antennaeof the same directivejcharacteristics spaced about 1,000

feetapart.

v Itwill be clear thatvarious modificationsv ofthearrangementdescribedand illustrated V have been shown.

by Figs. 1 and-2 and the description thereof maybe made insofar as theyfall fairlywith-' in the scope of'the invention as defined by thefollowing claims. j

Havingthus described our invention, what weclaimis;", V i 1. The methodof avoiding theefi'ects' of fading on radio signals which includes, receiving the samesignal at a pluralityof separated points, separatelyrectifying the signal so received to produce current pulses of :lessthan the received radio frequency, commeans for combining the outputs ofsaid r'ectifiers, said means including .aiesi'stangie in the combiningcircuit, a limiting device, means for controlling the operation of saidlimiting device by the resistance drop occurring in saidresistance' whensignals are received, a modulator, a tone circuit,and means provided bysaid limiting device for limiting the iresponse of saidomodulator insaid tone circuit to a substantially constant value irre-v 1 'spectiveof moderate intensity variations.

when signals are being received upon said antenna members and thecomblned rect fied signals produce, a resistancedrop across saidvresistance equal to orgreater'than the lilmiting value ofsaidlimitingdevice. V j

. 3. In combination, in asystem for reducing fading, aplurality ofseparated energy collectors, means for reducing thefrequency'of energycollected on said collectors, means for combining the energies ofreduced frequency, an impedance, means for applying the com- 'binedenergies to said impedance whereby voltage variationsarise across saidimpedance in accordance'with the combined energies passed therethrough,an electron discharge device having an anode a cathode anda con- .trolelectrode, a source of undulatory-electromotive force coupled to theanode circuit of said electron discharge device, an output circuit'coupled to said anode circuit, andmeans for coupling said. impedance tothe control "electrode of said electron discharge device wherebycurrent,.corresponding in frequency to thealternating 'electromotiveforce generated flows'in said output circuit in accordance withthepotential applied to-said control electrode from said impedance.

4. In a systemof thecha-racter described,- anenergy collector forcollecting modulated high frequency electrical waves, means forobtaining currents corresponding to the modulation of said waves, aresistance, means for passing said modulation currents through saidresistance whereby potentials arise there across corresponding in valueto the currents applied, an electron discharge device having an anodecircuit and an output circuit coupled to said anode circuit, a localgenerator of alternating current coupled to said anode circuit, andmeans coupling said resistance and said electron discharge devicewhereby the internal impedance of said electron discharge device isvaried in accordance with the voltage variations across said resistance,whereby alternating current from said local source flows in said outputcircuit in varying degree as the conductivity of said electron dischargedevice is varied. HAROLD H. BEVERAGE.

HAROLD O. PETERSON.

